Method of cooling and granulating petroleum pitch



July 28, 1959 J. MCAFEE 2,896,261

METHOD OF COOLING AND GRANULATING PETROLEUM PITCH Filed Dec. 27, 1954 INV EN TOR.

BY W

JrraeA/Ew- METHOD OF COOLING AND GRANULATING PETROLEUNI PITCH JerryMcAfee, Oakmont, Pa., assignor to Gulf Research & Development Company,Pittsburgh, Pa., a corporation of Delaware Application December 27,1954, Serial No. 477,795

3 Claims. (Cl. 18-471) This invention relates to a process for coolingand solidifying petroleum pitches and more particularly to a process forthe preparation of granulated petroleum pitch particles from the liquidpitch.

The high rate of production of petroleum distillates during recent yearshas resulted in the production of large quantities of residual productsof low value. A process that has recently been developed to reduce theamount of residual products produced in the refining of petroleumconsists of preparing a solid petroleum pitch of low hydrogen to carbonratio and thereby increasing the amount of distillate available as acharge stock to catalytic cracking processes. Processes in which theresidual product is a pitch have an important advantage over cokingprocesses, which also produce solid residual products, in that thepitches are liquid at high temperatures and may easily be removed fromthe equipment. The pitches can be prepared by an extremely deep vacuumreduction of certain types of crudes or by visbreaking of very heavyoils in combination with deep reduction of the visbroken material.

While the yield of pitch from most crudes may be relatively small, theextremely large crude oil runs in refineries will result in theproduction of large amounts of pitch. The principal use of the pitch isas a fuel. If the pitch can be used near its place of manufacture, itmay be maintained and transported in the liquid form. However, the highsoftening point of the pitch, which generally ranges from 275 to 450 F,makes its transportation as a liquid difficult, except for shortdistances. It is, therefore, desirable to solidify the pitch in a formwhich can be easily handled and transported to points of use.

According to this invention, a dispersion of liquid water and petroleumpitch is formed at temperatures sufficiently high above the softeningpoint of the pitch to maintain it in a fluid condition and thedispersion is then flashed by a sudden reduction in the pressure towhich it is subjected whereupon evaporation of the water cools andsolidifies the pitch to form a finely divided solid product.

The single figure of the drawing is a schematic flowsheet illustratingapparatus suitable for use in the process of this invention.

The pitch to be treated according to this invention is ordinarilywithdrawn from a distillation tower and used directly in thissolidification process. The temperature of the dispersion of pitch andwater must be below the critical temperature of water in order thatthere will be a rapid change in phase of the water upon flashing and thelatent heat of vaporization of the water will be sufliciently large toextract substantial quantities of heat from the pitch. Hence, it may benecessary to cool the pitch prior to mixing with water. A pitch feedstock temperature in the range of 500 to 700 F. is preferred.

The water mixed with the pitch is preferably heated to approximately thesame temperature as the pitch prior to mixing in order to facilitate themixing. However, it is only necessary that a dispersion of pitch andwater be made at a temperature high enough that the pitch-remainsPatented July 28, 1959 fluid and easily handled as a liquid and at apressure high enough to maintain enough water in the liquid phase thatupon reduction of the pressure the extraction of the latent heat ofvaporization of the liquid water from the pitch will solidify it; Thetemperature of the dispersion of pitch and water is preferably intherange of 500 to 600 F., and the pressure maintained on the dispersionwhen the temperature is in the preferred range is consequently in therange of approximately 700 to 1600 p.s.i.g. Cooling of the pitch orpreheating of the water is not essential as long as a substantiallyuniform dispersion of water and pitch falling within the conditionsdefined above is obtained. A

A wide range of ratios of water to pitch may be employed. It is onlyessential that there be sufficient Water present as a liquid in thedispersion that vaporization of the water upon reduction of the pressurewill extract sufficient heat from the pitch to solidify the pitch andcool it to a temperature at which it Will not cake nor agglomerate.Water in excess of that required is not a serious disadvantage since theexcess water is readily drained from the solidified pitch. For instance,experimental runs have been made in which the ratio of water to pitch,on a volume to volume basis, has been varied from 0.38 to l to 1.4 to 1without deleterious effects on the pitch.

It is important that the water and pitch be thoroughly mixed at the hightemperature and pressure while the water is in the liquid phase. Asubstantially uniform dispersion, for example, an emulsion of the twoliquids, is required to insure uniform cooling of all of the pitch byliberation of the heat of vaporization of the water. As a result, thepitch particles are substantially uniformly po rous, indicating flashingof water to steam uniformly throughout the pitch and large masses ofpartially cooled and solidified pitch, which might clog the separatingequipment, are not formed.

The product of this invention is a particulate solid material. The pitchparticles are porous and brittle and may easily be ground to finer sizesif desired as, for example, when the pitch is to be used as a powderedfuel. By adjustment of the conditions at @which the flashing of thewater from the pitch occurs, particle sizes may be controlled in therange from fines having particle sizes below about one-sixteenth inch indiameter to particles one-half to three-fourths of an inch in diameter,or even larger. For example, by adjustment of the conditions during theflashing of the water from the pitch, particles of roughly cylindricalshape which swell to about one-half of an inch in diameter can beextruded continuously from a tube one-eighth inch in diameter. Theselarge particles swell, become distorted, and break into segments as theyare discharged from the tube, but like the finely divided particles, areporous and brittle. At other conditions, notably higher velocities inthe tubing, fines of about one-sixteenth inch in diameter can bedischarged as discrete particles from tubing of the same size.

Referring to the drawing, water for cooling the pitch is introducedthrough lines 10 and 12 to a pump 14 which pumps the water to a pressuresufficiently high to maintain a major portion of the water in the liquidphase during the subsequent heating and mixing opera tions. Pump 14 isof any type suitable for pumping the water to the high pressures in therange of about 700 to 3100 p.s.i. required to maintain the water in theliquid phase, and in the apparatus illustrated is of the piston type.The compressed water is discharged through a line 16 into a preheater18, in which the water is raised to a temperature such that when mixedwith molten pitch will form a mixture in the temperature range of about'450 to 700 F. and preferably 500 to 600 F. In the preferred mode ofoperation, the water is heated to substantially the same temperature asthe pitch to facilitate mixing of the two liquids. The heated water isdischarged from the preheater 18 through a line 20 to a mixer 22.

Pitch to be solidified is supplied through a line 24 to a pump 26 whichis also illustrated as being of the piston type. The pitch is dischargedfrom the pump 26 through a line 28 which delivers the pitch into line20. The pitch feed stock in line 24 may be obtained directly from thebottom of a vacuum tower in which the pitch is formed. If thetemperature of the pitch is too high, and will form a mixture of waterand pitch having a temperature above the critical temperature of water,or higher than desired for other reasons, it may be passed throughsuitable heat exchanger apparatus, not shown, in which its temperatureis reduced to the preferred range of about 500 to 700 F. For example,the pitch may be passed in indirect heat exchange with the water tosupply at least a part of the heat required to raise the temperature ofthe water to the desired level prior to mixing.

The mixture of preheated water and pitch from line 20 passes throughmixer 22 in which a substantially uniform dispersion of the pitch inwater, such as an emulsion of the two liquids, is formed. The mixer 22can be of any type suitable for the formation of the desired dispersion.In the apparatus illustrated in the drawings, the mixer is an elongateddrum provided with a plurality of baffles 30 which create the turbulencenecessary for the formation of the dispersion. A simple tube of asufficiently small diameter to cause a highly turbulent flow within thetube and of suflicient length to accomplish thorough mixing is anotherexample of apparatus that is suitable.

The conditions maintained within the mixer 22 are such that the majorportion of the water is present in the liquid phase. Since thetemperature of the mixture must be high enough to maintain the pitch ina fluid, easily pumped condition, the minimum temperature will bedetermined in part by the softening point of the pitch. Temperatures ofat least about 450 F. and preferably in the range of approximately 500to 600 F., and pressures ranging from about 700 pounds to as high as thecritical pressure of water, and preferably from approximately 700 p.s.i.to approximately 1600 p.s.i., are maintained at the discharge end of themixer 22.

The dispersion of water and pitch is throttled through a pressurecontrol valve 32 in which the pressure on the mixture is rapidlyreduced, thereby causing flashing of the liquid water. The mixture, atthe greatly reduced pressure, is discharged through the control valve 32and passes through line 34 into separator 36 maintained at substantiallyatmospheric pressure, for example, up to 50 p.s.i. absolute. Water vaporformed as a result of the flashing of the water in the dispersion isdischanged from the separator 36 overhead through a line 38 andpreferably vented to the atmosphere through a line 40. The finelydivided solid pitch particles are formed as a result of the extractionof heat from the pitch to supply the heat of vaporization of the water,fall to the bottom of the separator 36, and are discharged through aline 42. If water in excess of the amount required to cool the pitch isemployed, the liquid water is collected at the bottom of the separator36 and is removed with the pitch through line 42.

The size of the pitch particles can be controlled by regulation of thevelocity of the mixture discharged from the control valve 32. At veryhigh velocities the turbulence of the mixture is so great and theflashing of liquid Water upon reduction of the pressure is so violentthat .the pitch mass is thoroughly broken up to form fines of a porous,brittle pitch in particles having a diameter of approximatelyone-sixteenth of an inch and smaller.

If the velocity of the material passing through the line 34 is reducedsufliciently, the mass of pitch in the line is not completely broken upand the pitch forms a substantially continuous highly, and uniformly,porous mass moving through the line 34 and discharged into the separator36. The high degree of disperson of the pitch and water prior toflashing results in the pitch being uniformly cooled, even at relativelylow velocities of discharge from the throttling valve into theseparator, and prevents caking or agglomeration in the separator. Thecooled pitch is brittle, and breaks up into short segments whendischarged into the separator 36. The velocity through the line 34 canbe controlled by the injection of an inert gas into the mixer 22, forexample, through a line 37, by control of the diameter of the line 34,or by control of the heat supplied to the pitch and water to regulatethe quantities of steam present in the mixer, as long as suflicientwater is present in the liquid phase to supply the necessary cooling.

If desired, the water vapor flashed from the pitch can be recycled forfurther use by passing the steam from line 38 through line 44 to acondenser 46 in which the steam is condensed. A pump 48 returns thecondensed steam through a line 50 to the inlet line 12 of pump 14.

The following examples illustrate specific applications of thisinvention for the production of pitch particles of different sizes.

Example] Water was heated to a temperature of 400 to 500 F. at apressure that varied between 1100 and 1400 p.s.i.g. and introduced intoa mixer at a rate of 5500 cc. per hour. Liquid petroleum pitch having aRing and Ball softening point of 280 F. was introduced at a temperatureof 550 F. into the mixer at the rate of 7200 cc. per hour. The mixerconsisted of an elongated section of tubing in which the turbulent flowof the two liquids in the tubing produced a thorough dispersion of thetwo liquids. The resulting mixture at a temperature of approximately 500F. was throttled through a valve and discharged through an ejectorconsisting of 6 inches of one-quarter inchpipe into a separator. Thepitch was extruded as a continuous string from the outlet of the ejectorand then quickly broken into particles of approximately three-quarterinch in diameter.

Example II The procedure described in Example I was repeated with theexception that the water was introduced into the mixer at a rate of 7200cc. per hour and the thoroughly mixed Water and pitch after throttlingthrough a pressure control valve were discharged through an ejector 4inches long and one-eighth inch in diameter. The solid pitch wasin theform of fines of a size less than approximately one-eighth inch indiameter.

Example III Water was introduced into a mixer at the rate of 7200 cc.per hour for admixture with pitch which was introduced at the same rateto form a dispersion of two liquids at a temperature of 500 F. and apressure varying between 1100 and 1400 p.s.i.g. Five hundred cubic feetof nitrogen per barrel of pitch were introduced into the mixer and theresulting mass discharged directly from a throttling valve into aseparator. The pitch formed was primarily in particles one-eighth inchin diameter mixed with some smaller particles.

Example IV The process described in Example III was repeated with theexception that the nitrogen was introduced into the mixer at the rate of1600 cubic feet per barrel of pitch instead of 500 cubic feet. The pitchparticles formed in the separator were substantially all fines less thanone-eighth inch in diameter.

The process of this invention provides an economical method ofsolidifying a petroleum pitch directly in particles of a size permittingeasy subsequent handling. Large amounts of pitch may be solidified witha minimum of equipment occupying a small space. Throughout the processthe pitch is either in a fluid condition or in the form of a highlydispersed solid which eliminates the formation of large solid masseswhich might plug the equipment.

I claim:

1. A process of solidifying hot liquid petroleum pitch having asoftening point above about 275 F. comprising mixing the hot liquidpitch at a temperature of about SOD-700 F. with water to form a mixturehaving a temperature above about 450 F. and below the criticaltemperature of water, the mixing being performed at an elevated pressureat least high enough to maintain water in the liquid phase at thetemperature of the mixture and below about 3100 p.s.i.g., the ratio ofwater to pitch being high enough that evaporation of the water onflashing at atmospheric pressure will extract suflicient heat tosolidify the pitch, agitating the mixture of water and liquid petroleumpitch while at the elevated temperature and pressure to form asubstantially uniform dispersion of water and pitch, and flashing theresulting mixture of pitch and water to substantially atmosphericpressure, whereby evaporation of the water cools the pitch to aatmperature below its softening point to form solid pitch particles.

2. A process as set forth in claim 1 in which an inert gas is mixed withthe pitch and water at the elevated temperature and pressure before theflashing to atmospheric pressure.

3. A process as set forth in claim 1 in which the ratio of water topitch is in the range of 0.38:1 to 1.4:1.

References Cited in the file of this patent UNITED STATES PATENTS1,285,358 Perry Nov. 19, 1918 1,660,403 Turkington Feb. 28, 19281,911,860 Wahlgren May 30, 1933 2,136,208 Fehr Nov. '8: 1938 2,464,187Seaton Mar. 8, 1949 2,551,452 Moss May 1, 1951 2,572,321 Deanesly Oct.23, 1951 2,691,625 Clarke Oct. 12, 1954 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent NO. 2,896,261 July 28, 1959 JerryMcAfee It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 5, line 13, for "process of" read process for line 23, for'flashing at" read flashing to column 6, line 6, for "atmperature" readtempera-cure =0 Signed and sealed this 8th day of December 1959o (SEAL)Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner ofPatents

